The invention relates to improvements in liquid-cooled engines, and more particuarly to improvements in internal combustion engines of the type wherein lubricant also serves as a medium for cooling various component parts of the engine.
German Offenlegungsschrift No. 35 09 095 discloses an engine wherein the lubricating circuit branches off the cooling circuit. This publication proposes to maintain the temperature of lubricant at a high level. German Pat. No. 648,930 discloses discrete lubricating and cooling circuits as well as discrete sources of lubricant and cooling medium. The patent also proposes to maintain the temperature of coolant at a high level.
German Pat. No. 658,055 and German Offenlegungsschrift No. 26 49 562 disclose engines wherein the cooling circuit branches off the lubricating circuit, i.e., there is a single path for the flow of lubricant from the source to the locus of diversion of some lubricant from the main stream of lubricant for the purpose of cooling. These publications further propose the utilization of a relief valve in order to maintain the "lubricating" lubricant at a pressure deviating from the pressure of lubricant which is to be used as a cooling medium. Thus, save for the engine of German Pat. No. 648,930, all of the above-enumerated publications propose a common source of lubricant, a first path for the circulation of lubricant for the purposes of lubrication, and a second path for the circulation of lubricant for the purposes of cooling whereby the two paths include a relatively long or very long common portion.
Numerous additional prior proposals deal with the mode of returning lubricant to the sump of an internal combustion engine. For example, the aforementioned German Offenlegungsschrift No. 26 49 562 and British Pat. No. 194,907 propose to control the flow of coolant (normally oil) with a pressure relief valve so that the coolant can flow through a heat exchanger or through a bypass and directly into the sump. The aforementioned German Offenlegungsschrift No. 35 09 095 proposes to employ a thermostatically controlled valve which regulates the return flow of coolant, either by way of a heat exchanger or directly through a bypass. This publication further proposes the provision of a second heat exchanger which can be used as a means for heating the driver's cabin or the passenger compartment of a motor vehicle and which can receive returning coolant ahead of or by way of the thermostatically controlled valve.